Control device of AC motor

ABSTRACT

A control device of a three-phase AC motor includes: an inverter for driving the motor; a current sensor for sensing a sensor phase current of the motor; and a controller for controlling the motor. The controller includes: a current estimation device for estimating d-axis and q-axis current estimated values based on the sensor phase current and an electric angle of the motor; and a zero-crossing interpolation device for interpolating the d-axis and q-axis current estimated values by fixing the d-axis and q-axis current estimated values when the sensor phase current is in a zero cross range, which includes a zero point, so that the sensor phase current crosses the zero point, and for outputting interpolated d-axis and q-axis current estimated values as fixed d-axis and q-axis values, which are used for a feedback control relating to current flowing through the motor.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2013-170193filed on Aug. 20, 2013, the disclosure of which is incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to a control device of an AC motor thatsenses a phase current of one phase among three phases by a currentsensor and that controls a current flowing through an AC motor.

BACKGROUND

In recent years, from a social requirement of a lower fuel consumptionand a less exhaust emission, an electric vehicle and a hybrid vehicle,each of which is mounted with an AC motor as a power source of avehicle, is drawing attention. For example, in some of the hybridvehicles, a DC power source made of a secondary battery or the like andan AC motor are connected to each other via an electric power conversionunit constructed of an inverter and the like, and a DC voltage of the DCpower source is converted into an AC voltage by the inverter to therebydrive the AC motor.

In the control device of the AC motor mounted in the hybrid vehicle andthe electric vehicle has been known the following technology (refer to,for example, a patent document 1): that is, a current sensor for sensinga phase current is provided only in one phase; and a current estimatedvalue estimated on the basis of a current sensed value of the one phaseis fed back, whereby a current flowing through an AC motor iscontrolled. Since the current sensor is provided only in the one phase,the number of the current sensor is reduced and the size of a portionnear a three-phase output terminal of an inverter is reduced and thecost of a control system of the AC motor is reduced.

In the technique disclosed in the patent document 1, on the basis of acurrent sensed value of one phase (for example, U phase), which issensed by the current sensor, and a d axis current command value and a qaxis current command value and an electric angle of an AC motor, thecurrent estimated values of the other two phases (for example, V phaseand W phase) are calculated.

Specifically, an angle (θ), which is formed by a rotator of the AC motorand a U phase axis of a stator, is added to a command current phaseangle (α), which is acquired from a d axis current command value id* anda q axis current command value iq* to thereby find a U phase currentphase angle θ′(=θ+α). Then, a current amplitude Ia is calculated by thefollowing formula (91) by the use of the U phase current phase angle θ′and a U phase current sensed value Iu. Then, a sin value at an electricangle shifted by ±120[°] from the U phase current phase angle θ′ ismultiplied by the current amplitude Ia to thereby calculate the currentestimated values Iv, Iw of the two other phases by the followingformulas (92), (93).Ia=Iu/[√(1/3)×{−sin(θ′)}]  (91)Iv=√(1/3)×Ia×{−sin(θ′+120°)}  (92)Iw=√(1/3)×Ia×{−sin(θ′+240°)}  (93)

Then, the current sensed value Iu of one phase and the current estimatedvalues Iv, Iw of the other two phases are dq transformed to therebycalculate a d axis current estimated value Id and a q axis currentestimated value Iq. Then, the current flowing through the AC motor iscontrolled by a current feedback control mode of feeding back the d axiscurrent estimated value Id and the q axis current estimated value Iq toa d axis current command value Id* and a q axis current command valueIq*.

In the technique of the patent document 1, when the U phase currentphase angle θ′=0[°] and sin(θ′)=0, in the calculation of the currentamplitude Ia by the formula (91), Iu is divided by 0, that is, “zerodivision” is caused and hence the current amplitude Ia cannot becalculated correctly. For this reason, the current estimated values Iv,Iw of the other two phases cannot be calculated correctly. However, thepatent document 1 never refers to measures against this “zero division”.

Further, when the current sensed value Iu=0 [A], from the formulas (92)and (93), the current estimated values Iv, Iw of the other two phasesare calculated as follows: Iv=0 [A] and Iw=0 [A]. Hence, there is apossibility that the control of the AC motor could not be performed.

Also in a technique other than the patent document 1, in the case wherea variable to become 0 in a specified phase or at a specified timing isincluded, there is a possibility that a correct calculation could beimpaired by “the zero division” of dividing something by 0 or “the zeromultiplication” of multiplying something by 0 and hence the currentestimated value could be varied.

[Patent document 1] JP-A 2004-159391

SUMMARY

It is an object of the present disclosure to provide a control device ofan AC motor that senses a phase current of one phase among three phasesby a current sensor and that controls a current flowing through an ACmotor and that prevents a current estimated value from being varied by“zero division” or “zero multiplication” in a calculation formula.

According to an aspect of the present disclosure, a control device of athree phase AC motor includes: an inverter for driving the AC motor; acurrent sensor for sensing a current flowing in a sensor phase amongthree phases of the AC motor as a sensor phase current; and a controllerfor switching on and off a plurality of switching elements, whichprovide the inverter, in order to control a current flowing through theAC motor. The controller includes: a current estimation device forestimating a d-axis current estimated value and a q-axis currentestimated value based on the sensor phase current and an electric angleof the AC motor; and a zero-crossing interpolation device forinterpolating the d-axis current estimated value and the q-axis currentestimated value, which are estimated by the current estimation device,by fixing the d-axis current estimated value and the q-axis currentestimated value when the sensor phase current is in a zero cross range,which includes a zero point, so that the sensor phase current crossesthe zero point, and for outputting an interpolated d-axis currentestimated value and an interpolated q-axis current estimated valuevalues as a fixed d-axis value and a fixed q-axis value, which are usedfor a feedback control relating to the current flowing through the ACmotor.

According to the above device, when the sensor phase current crosseszero, the d axis current estimated value and the q axis estimated valueare interpolated, so that it is possible to prevent “zero division” ofdividing something by 0 or “zero multiplication” of multiplyingsomething by 0 from being caused in a current estimation formula. Hence,it is possible to prevent the current estimated values from being variedwhen the sensor phase current crosses zero.

By zero-crossing interpolating the d axis current estimated value andthe q axis current estimated value “directly”, it is possible to preventthe d axis current estimated value and the q axis current estimatedvalue from being varied with more reliability as compared with a casewhere the d axis current estimated value and the q axis currentestimated value are indirectly interpolated. Hence, not only in thefeedback control using the d axis current estimated value and the q axiscurrent estimated value but also other control or determinationperformed by the use of the d axis current estimated value and the qaxis current estimated value, it is possible to avoid the effect of anerroneous determination and a malfunction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagram to show a construction of an electric motor drivesystem to which a control device of an AC motor according to anembodiment of the present disclosure;

FIG. 2 is a general construction diagram of the control device of an ACmotor according to the embodiment of the present disclosure;

FIG. 3 is a block diagram to show a construction of a control section ofa current feedback control mode according to a first embodiment of thepresent disclosure;

FIG. 4 is a block diagram to show a construction of another phasecurrent estimation part of FIG. 3;

FIG. 5 is a chart to illustrate a fixed coordinate system (α-βcoordinate system) based on a sensor phase;

FIGS. 6A and 6B are waveform charts to illustrate a movement of anotherphase current estimated value when a sensor phase current crosses zero;

FIG. 7 is a schematic chart to show an example of interpolating a d axisvoltage command value and a q axis voltage command value when a sensorphase current crosses zero;

FIG. 8 is a flow chart of current estimation processing according to thefirst embodiment of the present disclosure;

FIG. 9 is a subordinate flow chart of zero-crossing interpolationprocessing of another phase current estimated value;

FIG. 10 is a flow chart of current estimation processing according to amodified example of the first embodiment;

FIG. 11 is a block diagram to show a construction of a control sectionof a torque feedback control mode according to a second embodiment ofthe present disclosure;

FIG. 12 is a flow chart of current estimation processing according tothe second embodiment of the present disclosure; and

FIG. 13 is a flow chart of current estimation processing according to amodified example of the second embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of a control device of an AC motor according tothe present disclosure will be described on the basis of the drawings.

First, a construction common to a plurality of embodiments will bedescribed with reference to FIG. 1 and FIG. 2. An electric motor controldevice 10 as “a control device of an AC motor” according to anembodiment is applied to an electric motor drive system 1 for driving ahybrid vehicle.

[Construction of Control Device of AC Motor]

As shown in FIG. 1, the electric motor drive system 1 has an AC motor 2,a DC power source 8, and the electric motor control device 10. The ACmotor 2 is an electric motor for generating torque for driving thedriving wheels 6 of an electrically driven vehicle.

The AC motor 2 of the present embodiment is a three-phase AC motor of apermanent magnet synchronous type.

The electrically driven vehicle includes a vehicle for driving thedriving wheels 6 by an electric energy such as a hybrid vehicle, anelectric vehicle, and a fuel cell electric vehicle. The electricallydriven vehicle of the present embodiment is a hybrid vehicle providedwith an engine 3 and the AC motor 2 is a so-called motor generator(designated by “MG” in the drawings) having a function as an electricmotor for generating torque to drive the driving wheels 6 and a functionas a generator which is driven by the kinetic energy of the vehicle,transmitted from the engine 3 and the driving wheels 6, and which cangenerate electricity.

The AC motor 2 is coupled to an axle 5 via a gear 4, for example, atransmission. In this way, a driving force of the AC motor 2 rotates theaxle 5 via the gear 4 to thereby drive the driving wheels 6.

The DC power source 8 is an electricity storage device that can chargeand discharge electricity, for example, a secondary battery such as anickel metal hydride battery or a lithium ion battery, and an electricdouble-layer capacitor. The DC power source 8 is connected to aninverter 12 (refer to FIG. 2) of the electric motor control device 10,that is, the DC power source 8 is so constructed as to supplyelectricity to the AC motor 2 and to be supplied with electricity fromthe AC motor 2 via the inverter 12.

A vehicle control circuit 9 is constructed of a microcomputer and thelike and is provided therein with a CPU, a ROM, an I/O, and a bus linefor connecting these elements, all of which are not shown in thedrawings. The vehicle control circuit 9 controls the whole of theelectrically driven vehicle by software processing, which is performedby executing previously stored programs by the CPU, and by hardwareprocessing, which is performed by a dedicated electronic circuit.

The vehicle control circuit 9 is so constructed as to be able to acquiresignals from various kinds of sensors and switches such as anaccelerator signal from an accelerator sensor, a brake signal from abrake switch, a shift signal from a shift switch, and a vehicle speedsignal relating to a speed of the vehicle, all of which are not shown inthe drawings. Further, the vehicle control circuit 9 detects a drivingstate of the vehicle on the basis of these acquired signals and outputsa torque command value trq* responsive to the driving state to theelectric motor control device 10. Further, the vehicle control circuit 9outputs a command signal to an engine control circuit (not shown) forcontrolling the drive of the engine 3.

As shown in FIG. 2, the electric motor control device 10 includes theinverter 12, a current sensor 13, and a control section 15 as “a controlmeans”.

The inverter 12 has a boost voltage of the DC power source by a boostconverter (not shown) inputted thereto as a system voltage VH. Theinverter 12 has six switching elements (not shown) connected in a bridgemode. As to the switching element, for example, an IGBT (Insulated GateBipolar Transistor), a MOS (Metal Oxide Semiconductor) transistor, and abipolar transistor can be used. The switching elements are switched onand off on the basis of PWM signals UU, UL, VU, VL, WU, WL outputtedfrom a PWM signal generation part 25 of the control section 15, wherebythe drive of the AC motor 2 is controlled on the basis of three phase ACvoltages vu, vv, vw to be impressed on the AC motor 2

The current sensor 13 is provided in any one phase of the AC motor 2. Inthe present embodiment, the current sensor 13 is provided in a W phase.Hereinafter, the W phase in which the first current sensor 13 isprovided is referred to as “a sensor phase”. The current sensor 13senses a phase current of the W phase as a current sensed value iw_snsof the sensor phase and outputs the current sensed value iw_sns to thecontrol section 15.

Hereinafter, in the description of the present embodiment, thedescription will be made on the premise of a construction in which thesensor phase is the W phase. However, in the other embodiments, a Uphase or a V phase may be the sensor phase.

A rotation angle sensor 14 is provided near a rotor (not shown) of theAC motor 2 and senses an electric angle θe and outputs the sensedelectric angle θe to the control section 15. Further, the number ofrevolutions N of a rotor of the AC motor 2 is calculated on the basis ofthe electric angle θe sensed by the rotation angle sensor 14.Hereinafter, “the number of revolutions N of the rotor of the AC motor2” is simply referred to as “the number of revolutions N of the AC motor2”.

The rotation angle sensor 14 of the present embodiment is a resolver.However, in the other embodiments, the rotation angle sensor 14 may beother kind of sensor, for example, a rotary encoder.

The control section 15 is constructed of a microcomputer and the likeand is provided therein with a CPU, a ROM, an I/O, and a bus line forconnecting these elements, all of which are not shown in the drawings.The control section 15 controls an action of the AC motor 2 by softwareprocessing, which is performed by executing previously stored programsby the CPU, and by hardware processing, which is performed by adedicated electronic circuit.

According to the number of revolutions N of the AC motor 2 based on theelectric angle θe sensed by the rotation angle sensor 14 and to a torquecommand value trq* from the vehicle control circuit 9, the electricmotor control device 10 drives the AC motor 2 as an electric motor,whereby the AC motor 2 performs “a powering operation as an electricmotor” and consumes electricity, or drives the AC motor 2 as agenerator, whereby the AC motor 2 performs “a regenerating operation asa generator” and generates electricity. Specifically, according to thenumber of revolutions N and whether the torque command value trq* isplus or minus, the electric motor control device 10 switches the actionof the AC motor 2 into the following four patterns:

<1. Normal rotation/powering operation> when the number of revolutions Nis plus and the torque command value trq* is plus, the AC motor 2consumes electricity;

<2. Normal rotation/regenerating operation> when the number ofrevolutions N is plus and the torque command value trq* is minus, the ACmotor 2 generates electricity;

<3. Reverse rotation/powering operation> when the number of revolutionsN is minus and the torque command value trq* is minus, the AC motor 2consumes electricity; and

<4. Reverse rotation/regenerating operation> when the number ofrevolutions N is minus and the torque command value trq* is plus, the ACmotor 2 generates electricity.

In the case where the number of revolutions N>0 (normal rotation) andthe torque command value trq*>0, or the number of revolutions N<0(reverse rotation) and the torque command value trq*<0, the inverter 12converts a DC electricity supplied from the DC power source 8 to an ACelectricity by the switching operation of the switching elements andsupplies the AC electricity to the AC motor 2, whereby the AC motor 2 isdriven in such a way as to output torque (to perform a poweringoperation).

On the other hand, in the case where the number of revolutions N>0(normal rotation) and the torque command value trq*<0, or the number ofrevolutions N<0 (reverse rotation) and the torque command value trq*>0,the inverter 12 converts an AC electricity generated by the AC motor 2to a DC electricity by the switching operation of the switching elementsand supplies the DC electricity to the DC power source 8, whereby the ACmotor 2 performs a regenerating operation.

[Construction and Operation & Effect of Control Section]

Hereinafter, the construction and the operation, and effect of thecontrol section 15 will be described for each embodiment. A controlsection 151 of a first embodiment controls a current flowing through theAC motor 2 by a current feedback control mode, whereas a control section153 of a second embodiment controls a current flowing through the ACmotor 2 by a torque feedback control mode.

First Embodiment

The control section 151 of the first embodiment of the presentdisclosure will be described with reference to FIG. 3 to FIG. 10.

The current feedback control mode is a control mode for feeding back a daxis current estimated value id_est and a q axis current estimated valueiq_est to a d axis current command value id* and a q axis currentcommand value iq*, respectively, and includes a so-called sine wavecontrol mode and an overmodulated control mode.

As shown in FIG. 3, the control section 151 includes a dq axis currentcommand value operation part 21, a current subtractor 22, a PI operationpart 23, an inverse dq transformation part 24, a PWM signal generationpart 25, a current estimation part 301, and a current estimated valuezero-crossing interpolation part 28 as “a zero-crossing interpolationmeans”.

The dq axis current command value operation part 21 operates a d axiscurrent command value id* and a q axis command value iq* in a rotarycoordinate system (d-q coordinate system) of the AC motor 2 on the basisof the torque command value trq* acquired from the vehicle controlcircuit 9. In the present embodiment, the d axis current command valueid* and the q axis command value iq* are operated with reference to amap stored previously. In the other embodiments, the dq axis currentcommand value operation part 21 may be constructed in such a way thatthe d axis current command value id* and the q axis command value iq*are operated from a mathematical formula or the like.

The current subtractor 22 has a d axis current subtractor 221 and a qaxis current subtractor 222. The d axis current subtractor 221calculates a d axis current deviation Δid of a difference between the daxis current estimated value id_est, which is calculated by the currentestimation part 301 and is fed back, and the d axis current commandvalue id*. Further, the q axis current subtractor 222 calculates a qaxis current deviation Δiq of a difference between the q axis currentestimated value iq_est, which is calculated by the current estimationpart 301 and is fed back, and the q axis current command value iq*.

The PI operation part 23 has a d axis PI operation part 231 and a q axisPI operation part 232. The d axis PI operation part 231 calculates a daxis voltage command value vd* by a PI operation in such a way that thed axis current deviation Δid converges to 0 so as to make the d axiscurrent estimated value id_est follow the d axis current command valueid*. Further, the q axis PI operation part 232 calculates a q axisvoltage command value vd* by a PI operation in such a way that the qaxis current deviation Δiq converges to 0 so as to make the q axiscurrent estimated value iq_est follow the q axis current command valueiq*.

The inverse dq transformation part 24 transforms the d axis voltagecommand value (fixed value) vd*_fix and the q axis voltage command value(fix value) vq*_fix to a U phase voltage command value vu*, a V phasevoltage command value vv*, and a W phase voltage command value vw* onthe basis of the electric angle θe acquired from the rotation anglesensor 14.

The PWM signal generation part 25 calculates PWM signals UU, UL, VU, VL,WU, WL, which relate to switching on or off the switching elements ofthe inverter 12, on the basis of the three phase voltage command valuesvu*, vv*, vw* and the system voltage VH impressed on the inverter 12.When the switching elements of the inverter 12 are switched on or off onthe basis of the PWM signals UU, UL, VU, VL, WU, WL, the three phase ACvoltages vu, vv, vw are generated. Then, when the three phase ACvoltages vu, vv, vw are impressed on the AC motor 2, the drive of the ACmotor 2 is controlled in such a way that a torque corresponding to thetorque command value trq* is outputted.

The current estimation part 301 has another phase current estimationpart 31 and a dq transformation part 34. In the first place, in the casewhere an electric motor control device having the current sensors 13provided in two phases, a current of one remaining phase in which thecurrent sensor 13 is not provided can be easily calculated by theKirchhoff's law. In contrast to this, in the present embodiment havingthe current sensor 13 provided only in one phase (W phase), the otherphase current estimation part 31 of the current estimation part 301estimates a current of one phase among two phases of the U phase and theV phase in which the current sensor 13 is not provided. Hereinafter, aphase in which a current is estimated is referred to as “an estimatedphase”. The description of the present embodiment will be made on thepremise of a construction in which the estimated phase is the U phase.

The dq transformation part 34 dq transforms the current sensed valueiw_sns of the sensor phase and a current estimated value iu_est of theestimated phase, which is estimated by the other phase currentestimation part 31, to thereby calculate a d axis current estimatedvalue id_est and a q axis estimated value iq_est.

In this regard, in FIG. 3, a case in which the estimated phase is the Vphase will be shown in a parenthesis such as [iu(v)_est] for the otherphase current estimated value outputted to the dq transformation part 34from the other phase current estimation part 31 and, in the same way,[u(v)w→dq] for the dq transformation part 34.

Next, a construction will be described in which the other phase currentestimation part 31 estimates a current estimated value iu_est of theestimated phase. Here, in the current feedback control mode, the d axiscurrent command value id* and the q axis current command value iq* areused for the control. Hence, the other phase current estimation part 31of the present embodiment calculates the current estimated value iu_estof the estimated phase on the basis of the information on the currentsensed value iw_sns of the sensor phase, the electric angle θe, and thed axis current command value id* and the q axis current command valueiq*.

In particular, the present embodiment is characterized in that thecurrent estimated value iu_est of the estimated phase is calculated froma sensor phase reference current phase θx calculated on the basis of anα axis current iα and a β axis current iβ in an α-β coordinate system.

The other phase current estimation part 31 of the present embodiment, asshown in a detailed construction of FIG. 4, includes another phasecurrent reference value calculation part 32 and another phase currentzero-crossing interpolation part 33.

The other phase current reference value calculation part 32 acquires thed axis current command value id* and the q axis current command valueiq*, which are calculated by the dq axis current command value operationpart 21, and the electric angle θe, and calculates a current commandvalue iv* of the V phase, which is not the estimated phase, by aninverse dq transformation.

In this regard, in the case where the estimated phase is the V phase inthe other embodiment, the other phase current reference valuecalculation part 32 may calculate a current command value iu* of the Uphase or may calculate the current command values iu*, iv* of the Uphase and the V phase.

Next, the other phase current reference value calculation part 32calculates the α axis current iα and the β axis current iβ by the use ofthe V phase current command value iv* calculated in this manner and thecurrent sensed value iw_sns of the sensor phase and then calculates thesensor phase reference current phase θx defined in the α-β coordinatesystem.

As shown in FIG. 5, an α axis corresponds to an axis of the W phase ofthe sensor phase and a β axis is orthogonal to the α axis. The sensorphase reference current phase θx is an angle, which is formed by the αaxis and a current vector (Ia ∠θx) of a current amplitude Ia and issynchronous with the current sensed value iw_sns of the sensor phase. Inthe state of a normal rotation and a powering operation of a plustorque, the sensor phase reference current phase θx when a waveform of aW phase current iw crosses zero from minus to plus is 0[°], whereas thesensor phase reference current phase θx when the waveform of the W phasecurrent iw crosses zero from plus to minus is 180[°].

Here, the α axis current iα and the β axis current iβ, which are usedfor calculating the sensor phase reference current phase θx, will bedescribed. When the α axis current iα and the β axis current iβ areexpressed by the use of the respective phase currents iu, iv, iw, the αaxis current iα and the β axis current iβ are shown by formulas (1),(2). Here, K in the formulas is a transformation coefficient.

[Mathematical  formula  1] $\begin{matrix}{{i\;\alpha} = {K \times ( {{iw} - {\frac{1}{2} \times {iu}} - {\frac{1}{2} \times {iv}}} )}} & (1) \\{{i\;\beta} = {K \times ( {{\frac{\sqrt{3}}{2} \times {iu}} - {\frac{\sqrt{3}}{2} \times {iv}}} )}} & (2)\end{matrix}$

Further, as described above, the sum of instantaneous values of threephase currents iu, iv, iw becomes 0 by the Kirchhoff's law, that is, thefollowing formula (3) holds.iu+iv+iw=0   (3)

Here, when the formula (1) is deformed by the use of the formula (3),the following formula (4) is obtained.[Mathematical formula 2]iα=K×3/2×iw   (4)

In other words, as shown in the formula (4), the α axis current iα canbe calculated on the basis of only the W phase current iw of the sensorphase. Here, when the current sensed value iw_sns of the sensor phase isused as the W phase current iw, an α axis current sensed value iα_snscan be expressed by a formula (5).[Mathematical formula 3]iα_sns=K×3/2×iw_sns   (5)

Further, when the formula (2) is referred to, in the case where thecurrent command value iu* is used as the U phase current iu and thecurrent command value iv* is used as the V phase current iv, a β axiscurrent estimated value iβ_est can be expressed by a formula (6).

[Mathematical  formula  4] $\begin{matrix}{{i\beta\_ est} = {K \times ( {{\frac{\sqrt{3}}{2} \times {iu}^{*}} - {\frac{\sqrt{3}}{2}{iv}^{*}}} )}} & (6)\end{matrix}$

In the formula (6), the β axis current estimated value iβ_est iscalculated from the current command values iu*, iv* and does not includea component of the current sensed value iw_sns of the sensor phase,which is sensed by the current sensor 13. For this reason, the β axiscurrent estimated value iβ_est calculated by the formula (6) is notalways information reflecting an actual current with high accuracy.Hence, when the formula (6) is deformed in such a way that the β axiscurrent estimated value iβ_est includes the current sensed value iw_snsof the sensor phase by the use of the Kirchhoff's law (formula (3)), thefollowing formula (7) can be obtained.

[Mathematical  formula  5] $\begin{matrix}{{i\beta\_ est} = {K \times ( {{{- \sqrt{3}} \times {iv}^{*}} - {\frac{\sqrt{3}}{2}{iw\_ sns}}} )}} & (7)\end{matrix}$

As shown by the formula (7), when the β axis current estimated valueiβ_est is made to include the current sensed value iw_sns of the sensorphase, which is an actual current, it is possible to respond tovariations in control and hence to narrow a region in which a W phaseaxis component is small and is hard to converge. Hence, the accuracy ofthe β axis current estimated value iβ_est can be improved. In otherwords, a sensing accuracy of the sensor phase reference current phase θxcalculated by the use of the β axis current estimated value iβ_est canbe improved.

Subsequently, the sensor phase reference current phase θx is calculatedby a formula (8) on the basis of the α axis current sensed value iα_snscalculated by the formula (5) and the β axis current estimated valueiβ_est calculated by the formula (6) or the formula (7).

Here, in the case where the sensor phase reference current phase θx iscalculated by an arc tangent function (tan⁻¹) by the use of the formula(8), depending on the definition of the α axis current iα and the β axiscurrent iβ, there could be a case where the sensor phase referencecurrent phase θx does not become an angle synchronous with the sensorphase (W phase). This is caused by the definition of an axis (forexample, an interchange or a sign inversion of the α axis and the βaxis).

In this case, it is assumed that the calculation method can be changedas required in such a way that: the sensor phase reference current phaseθx when the current sensed value iw_sns of the sensor phase in a normalrotation and a normal torque crosses zero from minus to plus becomes0[°]; and the sensor phase reference current phase θx when the currentsensed value iw_sns of the sensor phase crosses zero from plus to minusbecomes 180[°], in other words, in such a way that the sensor phasereference current phase θx becomes an angle synchronous with the sensorphase current sensed value iw_sns. For example, the sensor phasereference current phase θx may be calculated after operating the signsof the α axis current iα and the β axis current iβ, or the α axiscurrent iα and the β axis current iβ may be interchanged between them,or a phase difference 90[°] caused by an orthogonal relationship betweenthe α axis and the β axis may be added to or subtracted from thecalculated sensor phase reference current phase θx.

[Mathematical  formula  6] $\begin{matrix}{{\theta\; x} = {\tan^{- 1}( \frac{i\beta\_ est}{i\alpha\_ sns} )}} & (8)\end{matrix}$

Next, the current estimated value iu_est of the U phase of the estimatedphase is calculated by the use of the sensor phase reference currentphase θx and the current sensed value iw_sns of the sensor phase. Here,when the current sensed value iw_sns of the sensor phase and the currentestimated value iu_est of the U phase of the estimated phase areexpressed by the use of the sensor phase reference current phase θx,because a phase difference between the respective phases is 120[°], thecurrent sensed value iw_sns of the sensor phase and the currentestimated value iu_est of the U phase of the estimated phase areexpressed by formulas (9) and (10), respectively. Here, Ia in theformulas (9), (10) is a current amplitude.iw_sns=Ia×sin(θx)   (9)iu_est=Ia×sin(θx−120°)   (10)

Further, when the formula (10) is deformed by the use of an additiontheorem, the U phase current estimated value iu_est can be expressed bythe following formula (11) by the use of the sensor phase referencecurrent phase θx and the current sensed value iw_sns of the sensorphase.

[Mathematical  formula  7] $\begin{matrix}\begin{matrix}{{iu\_ est} = {{Ia} \times {\sin( {{\theta\; x} - {120{^\circ}}} )}}} \\{= {{{- \frac{1}{2}} \times {Ia} \times {\sin( {\theta\; x} )}} - {\frac{\sqrt{3}}{2} \times {Ia} \times {\cos( {\theta\; x} )}}}} \\{= {{{- \frac{1}{2}} \times {iw\_ sns}} - {\frac{\sqrt{3}}{2} \times \frac{{Ia} \times {\sin( {\theta\; x} )}}{\tan( {\theta\; x} )}}}} \\{= {\{ {{- \frac{1}{2}} - {\frac{\sqrt{3}}{2} \times \frac{1}{\tan( {\theta\; x} )}}} ) \times {iw\_ sns}}}\end{matrix} & (11)\end{matrix}$

Further, when an estimation coefficient iu_kp is defined by a formula(12), the U phase current estimated value iu_est can be expressed alsoby a formula (13) by the use of the estimation coefficient iu_kp. Here,the estimation coefficient iu_kp may be directly operated by a formula(12), or a part or all of the formula (12) may be mapped in advance onthe basis of the sensor phase reference current phase θx and then theestimation coefficient iu_kp may be calculated with reference to thismap.

In the case where the control section 151 is constructed of aconventional electronic control circuit (microcomputer), when thecontrol section 151 is mounted with an operation formula, the operationformula is processed not in continuous time but in discrete time andhence the sensor-sensed value and the respective operated values aretreated also as discrete values based on a specified resolution (LSB).Here, “the control section 151 is mounted with an operation formula”means that the control section 151 includes a program of software and aconstruction of a hardware circuit. In order to avoid multiplication anddivision of large processing load, it is effective to map the estimationcoefficient iu_kp or a term of {1/tan (θx)} in the estimationcoefficient iu_kp by using the sensor phase reference current phase θxas an argument. This mapping makes it easy to apply the control section151 to a discrete system, which results in minimizing the processingload of the microcomputer and hence eliminating the need for using anexpensive microcomputer having a high operation processing capacity.

[Mathematical  formula  8] $\begin{matrix}{{iu\_ kp} = {{- \frac{1}{2}} - {\frac{\sqrt{3}}{2} \times \frac{1}{\tan( {\theta\; x} )}}}} & (12) \\{{iu\_ est} = {{iu\_ kp} \times {iw\_ sns}}} & (13)\end{matrix}$

When the formula (11) or the formula (13) is referred to, in the case ofcalculating the U phase current estimated value iu_est by the use of thesensor phase reference current phase θx and the current sensed valueiw_sns of the sensor phase, the current amplitude Ia is not used. Hence,in the current estimation, the current amplitude Ia does not need to befound and hence variables to be operated can be reduced.

The U phase current estimated value iu_est, which is calculated on thebasis of the sensor phase reference current phase θx and the currentsensed value iw_sns of the sensor phase, is outputted as a currentestimated value (reference value) iu_est_ref of the estimated phase tothe other phase current zero-crossing interpolation part 33.

Here, as shown in FIGS. 6A and 6B, the current sensed value iw_sns ofthe sensor phase changes in the shape of a sine wave and interchangesbetween plus and minus across 0 [A] every phase of 180[°]. In this way,not only when the current sensed value iw_sns of the sensor phase isstrictly 0 [A] but also when the current sensed value iw_sns of thesensor phase is within a specified range Az including 0 [A] is referredto as “when the sensor phase current crosses zero”. Further, in thefollowing descriptions, when the current value or the like includes notonly a value of strict 0 but also a value within a range substantiallyequivalent to 0 in terms of a control operation in which a sensing errorand the resolution of a device are taken into consideration, the currentvalue or the like will be described as “zero”.

“A value within a specified range Az including 0 [A]” means that anabsolute value of the current sensed value iw_sns of the sensor phase isnot more than a specified value or that an absolute value of theestimation coefficient iu_kp is not less than a specified value. Here,“a specified value” may be set by a current value of, for example, ±5[A], or may be set on the basis of a resolution of, for example, 5 [LSB]in the discrete system, or may be set by a mathematical formula or thelike. Further, since the current sensed value iw_sns of the sensor phaseis synchronous with the sensor phase reference current phase θx, “aspecified value” may be set by a value of the sensor phase referencecurrent phase θx.

As shown in FIG. 6B, a state where the current sensed value iw_sns ofthe sensor phase is within the specified range Az corresponds to azero-crossing phase range Pzx on a phase axis. The zero-crossing phaserange Pzx can be also converted to “a zero-crossing period Tzx” (referto FIG. 7 and the like, which will be described later) on a time axis.As for a method for converting the zero-crossing phase range Pzx to thetime axis, any method may be used: for example, a method for calculatingthe number of revolutions of the AC motor 2 as a coefficient, and amethod for measuring the time that elapses between two points of astarting point and an ending point of the zero-crossing phase range Pzxby a timer or the like in the microcomputer.

When the sensor phase current crosses zero, from the formula (5), an αaxis current sensed value iα_sns becomes zero and a tangent tan (θx) ofthe sensor phase reference current phase θx becomes infinite in theformula (8). Then, when the current sensed value iw_sns of the sensorphase becomes zero or the tangent tan (θx) of the sensor phase referencecurrent phase θx becomes infinite in the formula (11), “zeromultiplication” of multiplying something by zero” is caused. Further,when the tangent tan (θx) of the sensor phase reference current phase θxbecomes zero in the formula (11), “zero division” of dividing somethingby zero is caused. For this reason, the current estimated value iu_estof the U phase of the estimated phase might be varied.

Hence, in the present embodiment, the other phase current zero-crossinginterpolation part 33 interpolates the current estimated value(reference value) iu_est_ref to thereby mask the zero division and thezero multiplication.

In this regard, as to the zero division, in order to prevent the currentestimated value from being calculated to be an unintentional value bythe effect of the discrete system in the formula (13), it is possible totake measures against the zero division also by setting a limited valuefor the estimated coefficient iu_kp or for a term of {1/tan (θx)} in theestimated coefficient iu_kp. Further, in the case where the controlsection 151 is mounted with the formula (13), it is also effective tomap the estimated coefficient iu_kp or the term of {1/tan (θx)} of theestimated coefficient iu_kp. In this case, it is possible to takemeasures against the zero division also by setting a limited value inthe map.

The other phase current zero-crossing interpolation part 33 includes azero-crossing determination part 331 and a last value holding part 332.The zero-crossing determination part 331 determines whether or not thepresent time is the time “when the sensor phase current crosses zero”.In other words, when the current sensed value iw_sns of the sensor phaseis within the specified range Az including 0 [A], the zero-crossingdetermination part 331 determines that the present time is the time whenthe sensor current crosses zero.

In the case where the zero-crossing determination part 331 determinesthat the present time is not the time when the sensor phase currentcrosses zero, the zero-crossing determination part 331 outputs thecurrent estimated value (reference value) iu_est_ref calculated by theother phase current reference value calculation part 32, as it is, as acurrent estimated value (fixed value) iu_est_fix to the dqtransformation part 34.

On the other hand, in the case where the zero-crossing determinationpart 331 determines that the present time is the time when the sensorphase current crosses zero, the zero-crossing determination part 331acquires a current estimated value (interpolated value) iu_est_cmp fromthe last value holding part 332 and outputs the current estimated value(interpolated value) iu_est_cmp as the current estimated value (fixedvalue) iu_est_fix to the dq transformation part 34.

The last value holding part 332 holds a value of the last time inadvance, and in the case where the zero-crossing determination part 331determines that the present time is the time when the sensor phasecurrent crosses zero, the last value holding part 332 calculates thecurrent estimated value (interpolated value) iu_est_cmp and outputs thecurrent estimated value (interpolated value) iu_est_cmp to thezero-crossing determination part 331.

For example, the last value holding part 332 holds a specified number ofnearest previous current estimated values (fixed values) iu_est_fix,which are calculated previously, as current estimated values (heldvalues) iu_est_hld. Then, in the case where the zero-crossingdetermination part 331 determines that the present time is the time whenthe sensor phase current crosses zero, the last value holding part 332makes the current estimated value (held value) iu_est_hld, which is avalue of the last time or a value before the last time, the currentestimated value (interpolated value) iu_est_cmp (hereinafter, thisoperation is referred to as “zero-crossing interpolate, or“zero-crossing interpolation”) and outputs the current estimated value(interpolated value) iu_est_cmp to the zero-crossing determination part331.

Further, for example, the last value holding part 332 holds a specifiednumber of nearest previous d axis current estimated values id_est and qaxis current estimated values iq_est, which are previously calculated bythe dq transformation part 34, as d axis current estimated values (heldvalues) id_est_hld and q axis current estimated values (held values)iq_est_hld. Then, in the case where the zero-crossing determination part331 determines that the present time is the time when the sensor phasecurrent crosses zero, the last value holding part 332 calculates a Uphase estimated value as a current estimated value (interpolated value)iu_est_cmp by the inverse dq transformation of the d axis currentestimated values (held values) id_est_hld and the q axis currentestimated values (held values) iq_est_hld, which are the values of thelast time or the values before the last time, and outputs the currentestimated value (interpolated value) iu_est_cmp to the zero-crossingdetermination part 331.

In this way, when the sensor phase current crosses zero, byinterpolating the current estimated value iu_est of the estimated phase,a sudden variation in the current estimated value iu_est of theestimated phase, which is caused by “the zero division” or the “zeromultiplication” in the formula (11), can be avoided. In this regard, amethod of zero-crossing interpolating the current estimated value iu_estof the estimated phase, which is performed by the other phase currentzero-crossing interpolation part 33, may be a method other than themethod described above, or the zero-crossing interpolation of thecurrent estimated value iu_est of the estimated phase may be notperformed as required.

The dq transformation part 34 calculates the d axis current estimatedvalue id_est and the q axis current estimated value iq_est by the dqtransformation by the use of the current estimated values (fixed values)iu_est_fix acquired from the other phase zero-crossing interpolationpart 33, the current sensed value iw_sns of the sensor phase, and theelectric angle θe. The calculation of the d axis current estimated valueid_est and the q axis current estimated value iq_est in the dqtransformation part 34 will be described. First, a general formula ofthe dq transformation will be shown in the following formula (14).

[Mathematical  formula  9] $\begin{matrix}{\begin{bmatrix}{id\_ est} \\{iq\_ est}\end{bmatrix} = {{\sqrt{\frac{2}{3}}\begin{bmatrix}{\cos( {\theta\; e} )} & {\cos( {{\theta\; e} - {120{^\circ}}} )} & {\cos( {{\theta\; e} + {120{^\circ}}} )} \\{- {\sin( {\theta\; e} )}} & {- {\sin( {{\theta\; e} - {120{^\circ}}} )}} & {- {\sin( {{\theta\; e} + {120{^\circ}}} )}}\end{bmatrix}}\begin{bmatrix}{iu} \\{iv} \\{iw}\end{bmatrix}}} & (14)\end{matrix}$

Here, iv=−iu−iw by the Kirchhoff's law (refer to formula (3)), and wheniu=iu_est and iw=iw_sns are substituted for the formula (14), thefollowing formula (15) can be acquired. Here, in the present embodiment,the current estimated value (fixed value) iu_est_fix, which iszero-crossing interpolated, is used as the iu_est.

[Mathematical  formula  10] $\begin{matrix}\begin{matrix}{\begin{bmatrix}{id\_ est} \\{iq\_ est}\end{bmatrix} = {{\sqrt{\frac{2}{3}}\begin{bmatrix}{{\cos( {\theta\; e} )} - {\cos( {{\theta\; e} - {120{^\circ}}} )}} & {{\cos( {{\theta\; e} + {120{^\circ}}} )} - {\cos( {{\theta\; e} - {120{^\circ}}} )}} \\{{- {\sin( {\theta\; e} )}} + {\sin( {{\theta\; e} - {120{^\circ}}} )}} & {{- {\sin( {{\theta\; e} + {120{^\circ}}} )}} + {\sin( {{\theta\; e} - {120{^\circ}}} )}}\end{bmatrix}}\begin{bmatrix}{iu\_ est} \\{iw\_ sns}\end{bmatrix}}} \\{= {\sqrt{\frac{2}{3}} \times {{\sqrt{3}\begin{bmatrix}{\cos( {{\theta\; e} + {30{^\circ}}} )} & {- {\cos( {{\theta\; e} - {90{^\circ}}} )}} \\{- {\sin( {{\theta\; e} + {30{^\circ}}} )}} & {\sin( {{\theta\; e} - {90{^\circ}}} )}\end{bmatrix}}\begin{bmatrix}{iu\_ est} \\{iw\_ sns}\end{bmatrix}}}} \\{= {{\sqrt{2}\begin{bmatrix}{\sin( {{\theta\; e} + {120{^\circ}}} )} & {- {\sin( {\theta\; e} )}} \\{\cos( {{\theta\; e} + {120{^\circ}}} )} & {- {\cos( {\theta\; e} )}}\end{bmatrix}}\begin{bmatrix}{iu\_ est} \\{iw\_ sns}\end{bmatrix}}}\end{matrix} & (15)\end{matrix}$

As shown in the formula (15), the d axis current estimated value id_estand the q axis current estimated value iq_est can be calculated by thedq transformation by the use of the current values (sensed values orestimated values) of two phases among three phases. Hence, the otherphase current estimation part 31 needs to calculate only the currentestimated value of one phase (U phase) among two phases other than thesensor phase and does not need to calculate the current estimated valueof the other phase (V phase).

Returning to FIG. 3, the description will be made continuously. Thecurrent estimation part 301, as described above, estimates the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est.

Incidentally, when the sensor phase current crosses zero, if the otherphase current zero-crossing interpolation part 33 interpolates thecurrent estimated value iu_est of the estimated phase, there is apossibility that the d axis current estimated value id_est and the qaxis current estimated value iq_est are varied by the error of thecurrent estimated value iu_est caused by the interpolation and hencethat the current feedback control could be made unstable. Hence, thecurrent estimated value zero-crossing interpolation part 28zero-crossing interpolates the d axis current estimated value id_est andthe q axis current estimated value iq_est apart from the zero-crossinginterpolation relating to the current estimated value iu_est of theestimated phase, thereby preventing the d axis current estimated valueid_est and the q axis current estimated value iq_est from being varied.

The current estimated value zero-crossing interpolation part 28determines on the basis of the current sensed value iw_sns of the sensorphase and the electric angle θe whether or not the present time is thetime when the sensor phase current crosses zero, as is the case with thezero-crossing determination part 331 of the other phase currentzero-crossing interpolation part 33. Alternatively, the currentestimated value zero-crossing interpolation part 28 may use thedetermination result of the zero-crossing determination part 331.

In the case where the current estimated value zero-crossinginterpolation part 28 determines that the present time is not the timewhen the sensor phase current crosses zero, the current estimated valuezero-crossing interpolation part 28 feeds back the d axis currentestimated value id_est and the q axis current estimated value iq_est,which are operated by the current estimation part 301, as they are, asthe d axis current estimated value (fixed value) id_est_fix and the qaxis current estimated value (fixed value) iq_est_fix to the subtractor22.

On the other hand, in the case where the current estimated valuezero-crossing interpolation part 28 determines that the present time isthe time when the sensor phase current crosses zero, the currentestimated value zero-crossing interpolation part 28 fixes the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est, which are estimated by the current estimation part 301, andfeeds back the d axis current estimated value id_est and the q axiscurrent estimated value iq_est, which are fixed, as the d axis currentestimated value (fixed value) id_est_fix and the q axis currentestimated value (fixed value) iq_est_fix to the subtractor 22.

When the d axis current estimated value id_est and the q axis currentestimated value iq_est are fed back to the subtractor 22, the PIoperation part 23 calculates the d axis voltage command value vd* andthe q axis voltage command value vq* by the PI operation on the basis ofthe d axis current deviation Δid and the q axis current deviation Δiq.

A specific example in which the d axis current estimated value id_estand the q axis current estimated value iq_est are fixed, thereby beinginterpolated, will be described with reference to FIG. 7. A horizontalaxis of FIG. 7 designates time and a vertical axis designates voltage.The time of the horizontal axis correlates to the sensor phase referencecurrent phase θx. In other words, the zero-crossing phase range Pzx ofFIG. 6B corresponds to “a zero-crossing period Tzx” from a time ts whenthe sensor phase current starts crossing zero till a time to when thesensor phase current finishes crossing zero.

Current values shown by solid lines are the d axis current estimatedvalue id_est and the q axis current estimated value iq_est which areestimated by the current estimation part 301 in the time except for thezero-crossing period Tzx. In the zero-crossing period Tzx, the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est at the time ts when the zero-crossing period Tzx starts are fixedas shown by broken lines and are employed as a d axis current estimatedinterpolated value id_est_cmp and a q axis current estimatedinterpolated value iq_est_cmp.

As values, at which the d axis current estimated value id_est and the qaxis current estimated value iq_est are fixed, may be used values of thed axis current estimated value id_est and the q axis current estimatedvalue iq_est in a cycle in which it is determined that the sensor phasecurrent crosses zero, or the values of the d axis current estimatedvalue id_est and the q axis current estimated value iq_est in a cyclejust before when it is determined that the sensor phase current crosseszero or in a cycle before the cycle may be held as past values and thepast values may be used as the values at which the d axis currentestimated value id_est and the q axis current estimated value iq_est arefixed. Alternatively, other appropriate values may be used.

Next, a current estimation processing routine of the first embodimentwill be described with reference to FIG. 8 and FIG. 9. In thedescription of the following flow charts, a symbol S designates “step”.Further, as described above, in the present embodiment, a constructionhas been described by way of example in which the W phase is selected asthe sensor phase from among three phases and in which the U phase isselected as the estimated phase in which the current is estimated, sothat also in the description of the flow charts, the description will bemade on the premise of the construction described above.

A current estimation routine is repeatedly performed at specifiedoperation intervals during a period in which the power of the controlsection 151 is on. When the present routine is started, in the firststep S10, the current sensed value iw_sns of the sensor phase, which issensed by the current sensor 13, is acquired and the electric angle θeof the AC motor 2, which is sensed by the rotation angle sensor 14, isacquired.

Then, in the first embodiment, the reference value calculation part 32of the other phase current estimation part 31 calculates the α axiscurrent iα and the β axis current iβ in S22, S23 and then calculates thesensor phase reference current phase θx in S28.

In S22, the current command value iv* of the V phase is calculated bythe electric angle θe of the AC motor 2 and by the inversetransformation based on the d axis current command value id* and the qaxis current command value iq*. The V phase in this case is a phasewhich is not the estimated phase among two phases other than the sensorphase. Here, in the other embodiment, the current command values iu*,iv* of the U phase and the V phase may be calculated.

In S23, the α axis current iα_sns is calculated by the formula (5) bythe use of the current sensed value iw_sns of the sensor phase.

In S24, the β axis current iβ_est is calculated by the formula (7) bythe use of the current command value iv* of the other one phase and thecurrent sensed value iw_sns of the sensor phase.

In S28, the sensor phase reference current phase θx is calculated by theformula (8) by the use of the α axis current iα and the β axis currentiβ.

In S40, the current estimated value (reference value) iu_est_ref of theU phase is calculated by the formula (11) by the use of the sensor phasereference current phase θx and the current sensed value iw_sns of thesensor phase. At this time, the current estimated value (referencevalue) iu_est_ref of the U phase may be calculated by the formula (13)by the use of the estimated coefficient iu_kp, which is calculated bythe formula (12) or is acquired from the map, and the current sensedvalue iw_sns of the sensor phase.

In S50, the other phase current zero-crossing interpolation part 33performs interpolation processing when the sensor phase current crosseszero for the current estimated value (reference value) of the U phase.In a subordinate flow chart of FIG. 9, in S51, the zero-crossingdetermination part 331 determines whether or not the present time is thetime when the sensor phase current crosses zero. This determination ismade, for example, by determining whether or not the current sensedvalue iw_sns of the sensor phase is a value within the specified rangeAz including 0 [A].

In the case where it is determined in S51 that the present time is notthe time when the sensor phase current crosses zero (NO), the routineproceeds to S52 where the current estimated value (reference value)iu_est_ref of the U phase, which is calculated in S40, is outputted asit is, as the current estimated value (fixed value) iu_est_fix of the Uphase.

On the other hand, in the case where it is determined in S51 that thepresent time is the time when the sensor phase current crosses zero(YES), the routine proceeds to S54. In S54, the current estimated value(interpolated value) iu_est_cmp of the U phase is acquired from the lastvalue holding part 332 and then the current estimated value(interpolated value) iu_est_cmp of the U phase is outputted as thecurrent estimated value (fixed value) iu_est_fix of the U phase.

Returning to FIG. 8, in S60, the dq transformation part 34 dq transformsthe current sensed value iw_sns of the sensor phase and the currentestimated value iu_est of the U phase by the formula (15) on the basisof the electric angle θe to thereby calculate the d axis currentestimated value id_est and the q axis current estimated value iq_est.

Next, in S81 to S83, the current estimated value zero-crossinginterpolation part 28 performs interpolation processing of the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est when the sensor phase current crosses zero.

In S81, it is determined whether or not the present time is the timewhen the sensor phase current crosses zero. The determination result ofthe S51 may be used as this determination.

In the case where it is determined that the present time is not the timewhen the sensor phase current crosses zero (S81: NO), the routineproceeds to S82. In S82, the d axis current estimated value id_est andthe q axis current estimated value iq_est, which are estimated by thecurrent estimation part 301, are outputted, as they are, as the d axiscurrent estimated value (fixed value) id_est_fix and the q axis currentestimated value (fixed value) iq_est_fix. Then, the routine is finished.

On the other hand, in the case where it is determined that the presenttime is the time when the sensor phase current crosses zero (S81: YES),the routine proceeds to S83. In S83, the d axis current estimated valueid_est and the q axis current estimated value iq_est are fixed, and thed axis current estimated value id_est and the q axis current estimatedvalue iq_est, which are fixed, are outputted as the d axis currentestimated value (fixed value) id_est_fix and the q axis currentestimated value (fixed value) iq_est_fix. Then, the routine is finished.

Further, in a modified example shown by a flow chart of FIG. 10, inaddition to S83, S84 for fixing the d axis voltage command value vd*andthe q axis voltage command value vq*, which are operated by the PIoperation part 23, is performed. Here, the d axis voltage command valuevd* and the q axis voltage command value vq* correspond to “a commandvalue relating to a voltage of an AC motor” in the current feedbackmode.

The d axis voltage command value vd* and the q axis voltage commandvalue vq* may be fixed by forcibly reducing the d axis current deviationΔid and the q axis current deviation Δiq to zero. Alternatively, the daxis voltage command value vd* and the q axis voltage command value vq*may be held at their values before the time is when the zero crossingperiod Tzx starts, thereby being fixed.

Effects of First Embodiment

(1) The electric motor control device 10 of the present embodiment is adevice for sensing a phase current of one phase among three phases bythe current sensor 99 and for estimating phase currents of the other twophases. The current sensor 13 is provided only in the sensor phase andhence the number of the current sensor 13 can be reduced. In this way, aportion near a three-phase output terminal of the inverter 12 can bereduced in size and the cost of the electric motor control device 10 canbe reduced.

Further, by reducing the number of the current sensor 13 to one, theeffect of a gain error of the current sensor, which could be caused in aconventional control system of an AC motor using a plurality of currentsensors, can be eliminated. In this way, in the AC motor 2, an outputtorque variation caused by the gain error of the plurality of currentsensors can be eliminated, which leads to eliminating a vehiclevibration, for example, in the case of an AC motor for a vehicle and toremoving an element of reducing the product marketability of thevehicle.

(2) When a current flowing through the AC motor 2 is controlled by thecurrent feedback control mode in the electric motor control device 10having the current sensor 13 provided only in one phase, byinterpolating the current estimated value iu_est of the estimated phasewhen the sensor phase current crosses zero, a state can be avoided inwhich calculation cannot be performed because of “the zero division” and“the zero multiplication” in the formula (11). Hence, it is possible toprevent the current estimated value iu_est of the estimated phase frombeing suddenly changed.

(3) When the sensor phase current crosses zero, by fixing the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est, it is possible to prevent variations in the d axis currentestimated value id_est and the q axis current estimated value iq_est.Hence, in the feedback control and the other control and determinationperformed by the use of the d axis current estimated value id_est andthe q axis current estimated value iq_est, it is possible to avoid theeffect of an erroneous determination and a malfunction.

(4) As a method other than the present embodiment for estimating the daxis current estimated value id_est and the q axis current estimatedvalue iq_est when the sensor phase current crosses zero can beconsidered, for example, a method for dq transforming the currentestimated value (fixed value) iu_est_fix, which is acquired byzero-crossing interpolating the current estimated value iu_est of theestimated value, and the current sensed value iw_sns of the sensor phaseto thereby calculate the d axis current estimated value id_est and the qaxis current estimated value iq_est. This method is a method forindirectly zero-crossing interpolating the d axis current estimatedvalue id_est and the q axis current estimated value iq_est.

In contrast to this, the method of the present embodiment “directly”interpolates the d axis current estimated value id_est and the q axiscurrent estimated value iq_est, which are estimated by the currentestimation part 301, by the current estimated value zero-crossinginterpolation part 28. Hence, as compared with the indirectinterpolation method, the method of the present embodiment can preventthe variations in the d axis current estimated value id_est and the qaxis current estimated value iq_est with more reliability.

(5) As is the case with the modified example (refer to FIG. 10), whenthe sensor phase current crosses zero, by fixing and interpolating the daxis voltage command value vd* and the q axis voltage command value vq*in addition to fixing the d axis current estimated value id_est and theq axis current estimated value iq_est, the current feedback control canbe performed with more stability. In this regard, any one of the d axisvoltage command value vd* and the q axis voltage command value vq* maybe fixed.

(6) As a conventional technique for estimating the current of a phaseother than the sensor phase in an electric motor control device having acurrent sensor provided only in one phase, the technique described inthe patent document 1 (JP-A 2004-159391) is a technique for estimatingthe current of the phase other than the sensor phase on the basis of a daxis current command value and a q axis current command value.

By the way, a current vector of an AC motor follows a command currentvector while changing with respect to a command current vectorcorresponding to a current command value by the effect of a controlerror and a feedback control. For this reason, there is caused “adifference” between an actual current phase and a command current phaseand hence the command current phase does not become informationreflecting the actual current phase with high accuracy. In this point,the conventional technique of the patent document 1 does never take theactual current phase into consideration and calculates the currentestimated values of the other two phases by the use of a U phase currentphase angle found from a command current phase angle. Hence, especiallyin the case where a change in torque and a change in rotation speed arerequired, as is the case with an AC motor for a vehicle, the currentestimated values cannot be calculated with high accuracy, which causes apossibility that the control of the AC motor cannot be established.

In contrast to this, the current estimation part 301 of the presentembodiment calculates the sensor phase reference current phase θx on thebasis of the α axis current iα and the β axis current iβ in the fixedcoordinate system (α-β coordinate system) based on the sensor phase andhence can calculate an actual current phase θx based on the sensorphase. Further, the current estimation part 301 of the presentembodiment calculates the current estimated value iu_est of theestimated phase on the basis of the sensor phase reference current phaseθx and the current sensed value iw_sns of the sensor phase and hence cancalculate the current estimated value iu_est of the estimated phase withaccuracy in consideration of the effects of the higher harmonic wavecomponent of the actual current phase θx and variations usuallydeveloped.

(7) In the present embodiment in which the current flowing through theAC motor 2 is controlled by the use of the current feedback controlmode, the β axis current iβ is calculated by the formula (6) or theformula (7) on the basis of two phase current values among the currentcommand values iu*, iv* of the phases other than the sensor phase, whichcan be acquired by inverse dq transforming the d axis current commandvalue id* and the q axis current command value iq*, and the currentsensed value iw_sns of the sensor phase. In particular, it is preferablethat the β axis current iβ is calculated by the formula (7) on the basisof the current command values iv* of one phase other than the sensorphase and the current sensed value iw_sns of the sensor phase.

In this case, in the α-β coordinate system, “a region in which theeffect of the current sensed value is large and in which a calculationerror of the sensor phase reference current phase θx is small” can beexpanded. Hence, the effect of the current sensed value of the sensorphase can be included in the β axis current iβ. As a result, acalculation accuracy of the sensor phase reference current phase θx canbe improved. In this way, periodic control variations in the d axiscurrent and the q axis current can be reduced, and at a transient timewhen the current command values are changed or the like, a calculationaccuracy of the current estimated value iu_est, in other words,convergence to a true value of the current estimated value iu_est can beimproved.

Second Embodiment

Next, a control section 153 of a second embodiment of the presentdisclosure will be described with reference to FIG. 11 to FIG. 13. Inthe description of a control block diagram and a flow chart of thesecond embodiment, the substantially same constructions or thesubstantially same steps as the first embodiment will be denoted by thesame reference symbols and their descriptions will be omitted.

A torque feedback control mode is a control mode of feeding back atorque estimated value tr_est to a torque command value trq*.Specifically, a square wave control mode of controlling a phase of asquare wave voltage is known as a control mode of the torque feedbackcontrol mode (for example, refer to JP-A 2010-124544). Here, a squarewave in this case means a waveform of one pulse in one cycle of current.

As shown in FIG. 11, the control section 153 includes a torquesubtractor 52, a PI operation part 53, a square wave generator 54, asignal generator 55, a current estimation part 303, a torque estimationpart 56, and a voltage phase command value zero-crossing interpolationpart 57 as “a zero-crossing interpolation means”.

The torque subtractor 52 calculates a torque deviation Δtrq of adifference between a torque estimated value trq_est, which is fed backfrom the torque estimation part 56, and a torque command value trq*.

The PI operation part 53 calculates a voltage phase command value Vψ,which is a phase command value of a voltage vector, in such a way thatthe torque deviation Δtrq converges to 0 so as to make the torqueestimated value trq_est follow the torque command value trq*.

The square wave generator 54 generates a square wave on the basis of thevoltage phase command value Vψ and the electric angle θe and outputs a Uphase voltage command value vu*, a V phase voltage command value vv*,and a W phase voltage command value vw*.

The signal generator 55 generates voltage command signals UU, UL, VU,VL, WU, WL, which relate to switching on/off the switching elements ofthe inverter 12, on the basis of the U phase voltage command value vu*,the V phase voltage command value vv*, and the W phase voltage commandvalue vw* and outputs the generated voltage command signals UU, UL, VU,VL, WU, WL to the inverter 12.

The switching elements of the inverter 12 are switched on/off on thebasis of the voltage command signals UU, UL, VU, VL, WU, WL, wherebythree phase AC voltages vu, vv, vw are generated. Then, the three phaseAC voltages vu, vv, vw are impressed on the AC motor 2 and hence thedrive of the AC motor 2 is controlled so as to output torquecorresponding to the torque command value trq*.

The current estimation part 303 estimates the d axis current estimatedvalue id_est and the q axis current estimated value iq_est on the basisof the current sensed value iw_sns of the sensor phase, which is sensedby the current sensor 13, and the electric angle θe, which is acquiredfrom the rotation angle sensor 14.

In the torque feedback control mode, unlike the current feedback controlmode, the d axis current command value id* and the q axis currentcommand value iq* or the current command values iu*, iv* of the phases(U phase and V phase) other than the sensor phase, which can be obtainedby inverse dq transforming the d axis current command value id* and theq axis current command value iq*, cannot be used for the currentestimation. Hence, the current estimation part 303 of the presentembodiment estimates the d axis current estimated value id_est and the qaxis current estimated value iq_est on the basis of the information onthe current sensed value iw_sns of the sensor phase and the electricangle θe without using these current command values.

In particular, in the present embodiment, as is the case with the firstembodiment, first, the other phase current estimation part calculatesthe current estimated value iu_est of the estimated phase by the use ofthe α-β coordinate system. Here, the present embodiment is characterizedby focusing attention on that the α axis current iα and the β axiscurrent iβ are in the relationship between “a sine wave and a cosinewave” and that a phase difference between the α axis current iα and theβ axis current iβ is 90[°] and by calculating the β axis current iβ onthe basis of a differential value Δiα of the α axis current. Then, thepresent embodiment is characterized by dq transforming the currentsensed value iw_sns of the sensor phase and the current estimated valueiu_est of the estimated phase to thereby calculate the d axis currentestimated value id_est and the q axis current estimated value iq_est.

The differential value Δiα of the α axis current is calculated by thefollowing formula (16) on the basis of “an amount of change in the αaxis current iα to an electric angle movement Δθe [rad] between timingswhen the α axis current iα is calculated”, that is, “a differencebetween a value of this time and a value of the last time of the α axiscurrent iα”.Δiα=−{iα (n)−iα (n−1)}/Δθe   (16)

Here, the electric angle movement Δθe is a value of expressing anelectric angle movement from the current sensing timing of the last timeto the current sensing timing of this time by a unit of radian. Further,iα (n) is the value of this time of the α axis current iα and iα (n−1)is the value of the last time of the α axis current iα.

In this regard, the current sensing timing may be set at “a switchingtiming”, which is the timing when the switching elements of any onephase of the inverter 12 is switched on/off every electric angle 60[°],and at “an intermediate timing” between consecutive switching timings.

Further, in the case where an operation in the control section 153 isperformed in a discrete system, the differential value Δiα of the α axiscurrent iα is delayed by the half of the electric angle movement Δθewith respect to an actual β axis current iβ. It is preferable inconsideration of this point that a correction amount H, which isobtained by multiplying an average value of the value of last time andthe value of this time of the α axis current iα by the half of theelectric angle movement Δθe (Δθe/2), is calculated from a formula (17)and that the correction amount H is added to the differential value Δiαof the α axis current iα by a formula (18).H={iα (n−1)+iα (n)}/2×(Δθe/2)   (17)iβ_est=Δiα+H   (18)

Then, the sensor phase reference current phase θx is calculated by theformula (8) by the use of the α axis current iα and the β axis currentiβ. Here, in the case where a sign is reversed by the definition of theα axis current iα and the β axis current iβ in the formula (16), thesign may be operated if necessary in such a way as to be appropriate forthe calculation of “tan⁻¹ (iβ/iα)” by the formula (8). Alternatively, inthe case where as the result of the calculation, the sensor phasereference current phase θx is not synchronous with the current sensedvalue iw_sns of the sensor phase, not only the sign is operated but alsoa phase difference of 90[°] may be appropriately added to or subtractedfrom the calculated sensor phase reference current phase θx. This is thesame as the current feedback control mode.

Further, it is assumed that the other phase current estimation part ofthe current estimation part 303 of the present embodiment has the samedetailed construction as the other phase current estimation part 31 ofthe first embodiment shown in FIG. 4 except for a point that the otherphase current reference value calculation part 32 has the d axis currentcommand value id* and the q axis current command value iq* inputtedthereto. The other phase current reference value calculation part 32calculates the current estimated value (reference value) iu_est_ref ofthe estimated phase by the formula (11) or the formula (13) on the basisof the current sensed value iw_sns of the sensor phase and the sensorphase reference current phase θx. Then, when the sensor phase currentcrosses zero, the other phase current zero-crossing interpolation part33 (refer to FIG. 4) zero-crossing interpolates the current estimatedvalue iu_est of the estimated phase to thereby calculate the currentestimated value (fixed value) iu_est_fix of the estimated phase.

When the current estimated value (fixed value) iu_est_fix of theestimated phase is calculated in this way, the current estimation part303 calculates the d axis current estimated value id_est and the q axiscurrent estimated value iq_est by the formula (15).

The current estimated value zero-crossing interpolation part 58determines on the basis of the current sensed value iw_sns of the sensorphase and the electric angle θe whether or not the present time is thetime when the sensor phase current crosses zero, as is the case with thezero-crossing determination part 331 of the other phase currentzero-crossing interpolation part 33 (refer to FIG. 4). Alternatively,the current estimated value zero-crossing interpolation part 58 may usethe determination result of the zero-crossing interpolation part 331.

In the case where the current estimated value zero-crossinginterpolation part 58 determines that the present time is not the timewhen the sensor phase current crosses zero, the current estimated valuezero-crossing interpolation part 58 outputs the d axis current estimatedvalue id_est and the q axis current estimated value iq_est, which areestimated by the current estimation part 303, as they are, as the d axiscurrent estimated value (fixed value) id_est_fix and the q axis currentestimated value (fixed value) iq_est_fix to the torque estimation part56.

On the other hand, in the case where the current estimated valuezero-crossing interpolation part 58 determines that the present time isthe time when the sensor phase current crosses zero, the currentestimated value zero-crossing interpolation part 58 fixes the d axiscurrent estimated value id_est and the q axis current estimated valueiq_est, which are estimated by the current estimation part 303, andoutputs the d axis current estimated value id_est and the q axis currentestimated value iq_est, which are fixed, as the d axis current estimatedvalue (fixed value) id_est_fix and the q axis current estimated value(fixed value) iq_est_fix to the torque estimation part 56.

Here, a specific example of interpolating the d axis current estimatedvalue id_est and the q axis current estimated value iq_est by fixing thed axis current estimated value id_est and the q axis current estimatedvalue iq_est is the same as FIG. 7 of the first embodiment.

The torque estimation part 56 operates the torque estimated valuetrq_est by a formula (19) or a map or the like on the basis of the daxis current estimated value id_est and the q axis current estimatedvalue iq_est (omitted “_fix in the end), which are outputted as thefixed values from the current estimated value zero-crossinginterpolation part 58, and feeds back the torque estimated value trq_estto the torque subtractor 52.trq_est=p×{iq_est×ψ+(Ld−Lq)×id_est×iq_est}  (19)

Here, symbols are as follows:

p: number of pairs of poles of AC motor

Ld, Lq: d axis self inductance, q axis self inductance

ψ: armature interlinkage magnetic flux of permanent magnet

Subsequently, a current estimation processing routine of the secondembodiment will be described with reference to FIG. 12.

A flow chart of FIG. 12 is different from the flow chart of FIG. 8 ofthe first embodiment only in a point that the α axis current iα and theβ axis current iβ are calculated by S25 to S27 in place of S22 to S24.

In S25, the α axis current iα is calculated by the formula (5) by theuse of the current sensed value iw_sns of the sensor phase.

In S26, the differential value Δiα of the α axis current iα iscalculated by the formula (16) on the basis of a change amount of the αaxis current iα to the electric angle movement Δθe between the currentsensing timings of the α axis current iα.

In S27, the correction amount H is added to the differential value Δiαof the α axis current iα by the formulas (17), (18) to thereby calculatethe β axis current estimated value iβ_est.

In a modified example shown by a flow chart of FIG. 13, S85 of fixing avoltage phase command value Vψ is performed in correspondence to S84 ofFIG. 10 of the first embodiment. Here, the voltage phase command valueVψ corresponds to “a command value relating to a voltage of an AC motor”in the torque feedback control mode.

The voltage phase command value Vψ may be fixed by forcibly reducing thetorque deviation Δtrq to zero. Alternatively, the voltage phase commandvalue Vψ may be held at the voltage before the time ts when thezero-crossing period Tzx starts, thereby being fixed.

Effect of Second Embodiment

The second embodiment has the effects (1) to (4) of the first embodimentin common and has the following effect (5′) in place of the effect (5)of the first embodiment. Further, the second embodiment has an effect(8) specific to the second embodiment.

(5′) As is the case with the modified example (refer to FIG. 13), whenthe sensor phase current crosses zero, by fixing and interpolating thevoltage phase command value Vψ in addition to fixing the d axis currentestimated value id_est and the q axis current estimated value iq_est,the torque feedback control can be performed with more stability.

(8) In the present embodiment, when the control section 153 performs thetorque feedback control mode, the β axis current iβ can be calculated onthe basis of the differential value Δiα of the α axis current iα withoutusing the current command values iu*, iv* of the other phases. Hence,also in the torque feedback control mode, an optimal current estimationby the α-β coordinate system can be performed as is the case with thecurrent feedback control mode.

Other Embodiments

(A) A method by which the current estimation means estimates the currentestimated value iu(v)_est of the estimated phase, the d axis currentestimated value id_est, and the q axis current estimated value iq_est onthe basis of the current sensed value iw_sns of the sensor phase of onephase and the electric angle θe is not limited to the method based onthe α axis current iα and the β axis current iβ in the α-β coordinatesystem as the embodiment described above.

For example, in a current estimation method using a current commandvalue, the technique of the JP-A 2004-159391 (patent document 1) of aconventional technique may be employed if it can be understood that theeffect (6) of the first embodiment cannot be obtained.

Further, it is also recommended to employ a current estimation methodthat estimates a d-axis current estimated value id_est and a q axiscurrent estimated value iq_est without estimating a current estimatedvalue of a phase other than a sensor phase on the basis of the currentsensed value iw_sns of a sensor phase of one phase and the electricangle θe and that could cause “the zero division” or “the zeromultiplication” in an estimation operation for a specified phase or at aspecified timing.

A current estimation part of employing this method is constructed insuch a way as to, first, estimate the d axis current estimated valueid_est and the q axis current estimated value iq_est and then tocalculate a current estimated value of the other phase by the inverse dqtransformation, as required.

(B) The sensor phase for sensing the sensor current by the currentsensor may be not only the W phase of the embodiment described above butalso the U phase or the V phase. Further, the estimated phase forcalculating the current estimated value from the current sensed value ofthe sensor phase and the sensor phase reference current phase θx may benot only the U phase of the embodiment described above but also the Vphase or the W phase.

(C) “The current feedback control mode” is not limited to the sine wavePWM control mode or the overmodulated PWM control mode but may be anycontrol mode of using a current command value and feeding back a currentsensed value or a current estimated value based on the current sensedvalue to the current command value.

Further, “the torque feedback control mode” is not limited to the squarewave control mode of the embodiment described above but may be anycontrol mode of feeding back a torque estimated value based on thecurrent sensed value relating to the drive of an AC motor to the torquecommand value.

(D) The AC motor of the embodiments described above is the three-phaseAC motor of a permanent magnet synchronous type but may be an inductionmotor or another synchronous motor in the other embodiments. Further,the AC motor of the embodiments described above may be the so-calledmotor generator having a function as an electric motor and a function asa generator but may be not have the function as the generator in theother embodiment.

(E) The control device of the AC motor according to the presentdisclosure is not limitedly applied to the system having one set of aninverter and an AC motor as the embodiments described above but may beapplied to a system having two sets of an inverter and an AC motor.Further, the control device of the AC motor according to the presentdisclosure may be applied to a system of an electric train having aplurality of AC motors connected in parallel to one inverter.

(F) The control device of the AC motor according to the presentdisclosure is not limitedly applied to the AC motor of the hybridvehicle having the construction shown in FIG. 1 but may be applied to anAC motor of an electrically driven vehicle having any construction.Further, the control device of the AC motor according to the presentdisclosure may be applied to an AC motor other than the AC motor of theelectrically driven vehicle.

The above disclosure has the following aspects.

According to an aspect of the present disclosure, a control device of athree phase AC motor includes: an inverter for driving the AC motor; acurrent sensor for sensing a current flowing in a sensor phase amongthree phases of the AC motor as a sensor phase current; and a controllerfor switching on and off a plurality of switching elements, whichprovide the inverter, in order to control a current flowing through theAC motor. The controller includes: a current estimation device forestimating a d-axis current estimated value and a q-axis currentestimated value based on the sensor phase current and an electric angleof the AC motor; and a zero-crossing interpolation device forinterpolating the d-axis current estimated value and the q-axis currentestimated value, which are estimated by the current estimation device,by fixing the d-axis current estimated value and the q-axis currentestimated value when the sensor phase current is in a zero cross range,which includes a zero point, so that the sensor phase current crossesthe zero point, and for outputting an interpolated d-axis currentestimated value and an interpolated q-axis current estimated valuevalues as a fixed d-axis value and a fixed q-axis value, which are usedfor a feedback control relating to the current flowing through the ACmotor.

Here, “the AC motor” includes an AC-driven motor, a generator, and amotor generator. For example, a motor generator that is used as a mainunit of a hybrid vehicle and an electric vehicle and that generates atorque for driving driving wheels corresponds to “the AC motor”.Further, for example, an electric motor control device for driving themotor generator corresponds to “a control device of an AC motor”.

As a specific example of “a feedback control relating to a currentflowing through the AC motor”, in a current feedback control mode, thefixed values themselves acquired by fixing the d axis current estimatedvalue and the q axis current estimated value, which are outputted by thezero-crossing means, are fed back to a d axis current command value anda q axis current command value. Further, in a torque feedback controlmode, a torque estimated value is calculated on the basis of the fixedvalues of the d axis current estimated value and the q axis currentestimated value, which are outputted by the zero-crossing interpolationmeans, and the torque estimated value is fed back to a torque commandvalue.

As values, at which the d axis current estimated value and the q axiscurrent estimated value are fixed, may be used values of the d axiscurrent estimated value and the q axis current estimated value in acycle in which it is determined that the sensor phase current crosseszero, or the values of the d axis current estimated value and the q axiscurrent estimated value in a cycle just before when it is determinedthat the sensor phase current crosses zero or in a cycle before thecycle may be held as past values and the past values may be used as thevalues at which the d axis current estimated value and the q axiscurrent estimated value are fixed. Alternatively, other appropriatevalues may be used.

According to the present disclosure, when the sensor phase currentcrosses zero, the d axis current estimated value and the q axisestimated value are interpolated, so that it is possible to prevent“zero division” of dividing something by 0 or “zero multiplication” ofmultiplying something by 0 from being caused in a current estimationformula. Hence, it is possible to prevent the current estimated valuesfrom being varied when the sensor phase current crosses zero.

“When the sensor phase current crosses zero, the zero-crossinginterpolation means fixes the d axis current estimated value and the qaxis current estimated value which are estimated by the currentestimation means” means that the zero-crossing interpolation meansoutputs the d axis current estimated value and the q axis currentestimated value, which are fixed, as fixed values in place of the d axiscurrent estimated value and the q axis current estimated value, whichare newly estimated by the current estimation means at an operationtiming in a zero-crossing period. Further, this construction means thatthe zero-crossing interpolation means “directly” interpolates the d axiscurrent estimated value and the q axis current estimated value, whichare operated by the current estimation means. In other words, thisconstruction means to exclude, for example, a construction in which thezero-crossing interpolation means zero-crossing interpolates the d axiscurrent estimated value and q axis estimated value indirectly by dqtransforming the phase current estimated value, which is zero-crossinginterpolated in a former stage.

By zero-crossing interpolating the d axis current estimated value andthe q axis current estimated value “directly”, it is possible to preventthe d axis current estimated value and the q axis current estimatedvalue from being varied with more reliability as compared with a casewhere the d axis current estimated value and the q axis currentestimated value are indirectly interpolated. Hence, not only in thefeedback control using the d axis current estimated value and the q axiscurrent estimated value but also other control or determinationperformed by the use of the d axis current estimated value and the qaxis current estimated value, it is possible to avoid the effect of anerroneous determination and a malfunction.

Alternatively, the current estimation device may further estimate acurrent estimated value of a phase other than the sensor phase asanother phase current estimated value. When the sensor phase current isin the zero cross range, the current estimation device interpolates theanother phase current estimated value.

Alternatively, when the sensor phase current is in the zero cross range,the controller controls the current flowing through the AC motor in sucha manner that the controller feeds back the fixed d-axis value and thefixed q-axis value, which are output by the zero-crossing interpolationdevice, with respect to a d-axis current command value and a q-axiscurrent command value.

Alternatively, when the sensor phase current is in the zero cross range,the controller calculates a torque estimated value based on the fixedd-axis value and the fixed q-axis value, which are output by thezero-crossing interpolation device, and controls the current flowingthrough the AC motor in such a manner that the controller feeds back thetorque estimated value with respect to a torque command value.

Further, as described in the above cases, there are the followingconstructions in which the current estimation means “further estimates acurrent estimated value of a phase other than a sensor phase”. A firstconstruction is a construction in which: a current estimated value of aphase other than a sensor phase is calculated; and then the currentsensed value of the sensor phase and the current estimated value of theother phase are dq transformed to thereby calculate a d axis currentestimated value and a q axis current estimated value. A secondconstruction is a construction in which: the d axis current estimatedvalue and the q axis current estimated value are calculated; and then acurrent estimated value of the other phase is calculated by an inversedq transformation. Further, a construction in which these constructionsare combined to each other can be formed.

In this construction, when the sensor phase current crosses zero,preferably, the current estimated value of the other phase is furtherinterpolated to thereby prevent the current estimated value of the otherphase from being suddenly changed.

Alternatively, when the sensor phase current is in the zero cross range,the controller further fixes a command value relating to a voltage ofthe AC motor.

In addition, as described in the above case, when the sensor phasecurrent crosses zero, the command value relating to the voltage of theAC motor may be fixed. “The d axis voltage command value and the q axisvoltage command value” correspond to “the command value relating to thevoltage of the AC motor” in the current feedback control mode, whereas“the voltage phase command value” corresponds to “the command valuerelating to the voltage of the AC motor” in the torque feedback controlmode.

It is noted that a flowchart or the processing of the flowchart in thepresent application includes sections (also referred to as steps), eachof which is represented, for instance, as S10. Further, each section canbe divided into several sub-sections while several sections can becombined into a single section. Furthermore, each of thus configuredsections can be also referred to as a device, module, or means.

While the present disclosure has been described with reference toembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. The present disclosure isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the spirit and scope of the present disclosure.

What is claimed is:
 1. A control device of a three phase AC motorcomprising: an inverter for driving the AC motor; a current sensor forsensing a current flowing in a sensor phase among three phases of the ACmotor as a sensor phase current; and a controller for switching on andoff a plurality of switching elements, which provide the inverter, inorder to control a current flowing through the AC motor, wherein thecontroller includes: a current estimation device for estimating a d-axiscurrent estimated value and a q-axis current estimated value based onthe sensor phase current and an electric angle of the AC motor; and azero-crossing interpolation device for interpolating the d-axis currentestimated value and the q-axis current estimated value, which areestimated by the current estimation device, by fixing the d-axis currentestimated value and the q-axis current estimated value when the sensorphase current is in a predetermined zero cross range, which includes azero point, so that the sensor phase current crosses the zero point, andfor outputting an interpolated d-axis current estimated value and aninterpolated q-axis current estimated value values as a fixed d-axisvalue and a fixed q-axis value, which are used for a feedback controlrelating to the current flowing through the AC motor.
 2. The controldevice of an AC motor according to claim 1, wherein the currentestimation device further estimates a current estimated value of a phaseother than the sensor phase as another phase current estimated value,and wherein, when the sensor phase current is in the zero cross range,the current estimation device interpolates the another phase currentestimated value.
 3. The control device of an AC motor according to claim1, wherein, when the sensor phase current is in the zero cross range,the controller controls the current flowing through the AC motor in sucha manner that the controller feeds back the fixed d-axis value and thefixed q-axis value, which are output by the zero-crossing interpolationdevice, with respect to a d-axis current command value and a q-axiscurrent command value.
 4. The control device of an AC motor according toclaim 3, wherein, when the sensor phase current is in the zero crossrange, the controller further fixes a command value relating to avoltage of the AC motor.
 5. The control device of an AC motor accordingto claim 1, wherein, when the sensor phase current is in the zero crossrange, the controller calculates a torque estimated value based on thefixed d-axis value and the fixed q-axis value, which are output by thezero-crossing interpolation device, and controls the current flowingthrough the AC motor in such a manner that the controller feeds back thetorque estimated value with respect to a torque command value.